The power consumption of the whole equipment including a plurality of electrical devices increases and decreases according to the operation condition of each electrical device. The amount of the maximum power consumption which increases and decreases is referred to as the peak power amount, and the time period when the peak power amount appears is referred to as the peak power time period. The basic rate of a commercial power supply is set according to the peak power amount. Therefore, for equipment utilizing a commercial power supply, it is important to reduce the peak power amount for cost reduction.
With respect to the technology of reducing the peak power amount of the whole equipment including a plurality of electrical devices, as related arts for example, the techniques described in Patent Documents 1 and 2 are publicly known.
Of the two documents, Patent Document 1 discloses a power receiving system for controlling the electric power of the whole equipment of a factory, a standard family or the like where various electrical devices are installed such as electronic devices and the like. This power receiving system includes an AC power storage unit, a switch unit for switching between the AC power storage unit and a commercial power source, and a control device for controlling the switch unit by detecting the receiving power amount. This power receiving system takes the commercial power source alone as the power supply source when the full load of the equipment does not exceed the contract power amount, and makes up the insufficient amount of the receiving power for the load from the AC power storage unit when the receiving power of the equipment is about to exceed the contract power amount. By virtue of this, the power amount received from the commercial power source is restrained under the contract power amount. Further, when the full load fluctuates under the contract power amount after the peak power time period, the receiving power is utilized to charge the AC power storage unit while supplying power to the full load of the equipment. By virtue of this, it is possible to get prepared for dealing with the power peak of the next day with the charged AC power storage unit without the power consumption due to discharging beyond the time period of the peak power consumption.
Further, Patent Document 2 discloses a power management system composed of a plurality of client computers and a management server. According to an instruction from the management server, each client computer can be switched from a state of being operated by an external power supply to a state of being operated by a built-in secondary battery, and vice versa. Further, according to another instruction from the management server, each client computer controls whether or not to allow the external power supply to charge the battery. The management server carries out the following controls based on the power load information received from the power company.
The power load information shows a temporal load change of the power supplied by the power company. The management server notifies all client computers of the prohibitions of charging the secondary battery and utilizing the external power supply during the time period when the power load exceeds a second threshold value. According to this notification, each client computer operates on the secondary battery, and stops charging the same. Further, the management server notifies all client computers of the permission of charging the secondary battery and the prohibition of utilizing the external power supply during the time period when the power load is lower than or equal to the second threshold value but higher than a first threshold value. According to this notification, each client computer operates on the secondary battery, and charges the same with the external power supply. Furthermore, the management server notifies all client computers of the permissions of charging the secondary battery and utilizing the external power supply during the time period when the power load is lower than or equal to the first threshold value. According to this notification, each client computer operates on the external power supply, and charges the secondary battery as necessary with the external power supply.
Further, in order to prevent the peak power from changing rapidly, the management server divides the plurality of client computers into a number of groups, and sends the above notification to each group at different times. For the same reason, the plurality of client computers belonging to the same group having received the above notification carry out a control corresponding to the notification with a time lag between the times different from each other.
On the other hand, for example, Patent Document 3 discloses an electrical device with a function of reducing the peak power autonomously. This electrical device described in Patent Document 3 realizes the reduction of the power supply amount from a power supply unit during the peak time period by optimizing the power consumptions between the power supply unit and a secondary battery. In particular, Patent Document 3 exemplarily shows a computer device as an example of the electrical device, and describes the performance of the following control.
First, the computer device is composed of a number of subsystems such as a CPU, hard disks, an inverter, and the like. Next, at the start time of the peak power reduction period (at 13:00, for instance), all of the subsystems constituting the computer device transit to the first stage at which the power is supplied from the secondary battery. Then, the sustaining time of the secondary battery is calculated from the discharge current and remaining level of the secondary battery to determine whether or not the secondary battery is sustainable until the end time of the peak power reduction period. If sustainable, then the first stage is maintained. If not, then the device proceeds to the next second stage.
At the second stage, the discharge current of the secondary battery is decreased by changing the power supply source for some of the subsystems (the inverter, for instance) from the secondary battery to the power supply unit. Then, the sustaining time of the secondary battery is calculated from the discharge current and remaining level of the secondary battery to determine whether or not the secondary battery is sustainable until the end time of the peak power reduction period. If sustainable, then the second stage is maintained. If not, then the device proceeds to the next third stage.
At the third stage, the discharge current of the secondary battery is further decreased by changing the CPU to a low-speed mode. Then, the sustaining time of the secondary battery is calculated from the discharge current and remaining level of the secondary battery to determine whether or not the secondary battery is sustainable until the end time of the peak power reduction period. If sustainable, then the third stage is maintained. If not, then the device proceeds to the next forth stage.
At the forth stage, the discharge current of the secondary battery is further decreased by changing the power supply source for the CPU from the secondary battery to the power supply unit. At the same time, the CPU is returned from the low-speed mode to the normal mode. Then, the sustaining time of the secondary battery is calculated from the discharge current and remaining level of the secondary battery to determine whether or not the secondary battery is sustainable until the end time of the peak power reduction period. If sustainable, then the forth stage is maintained. If not, then the device proceeds to the next fifth stage (the final stage).
At the fifth stage, the power supply unit is utilized as the power supply source for all subsystems of the computer.
[Patent Document 1] JP 2006-230147 A
[Patent Document 2] JP 2004-180404 A
[Patent Document 3] JP 2003-150281 A
With respect to equipment including a plurality of electrical devices, it is possible to reduce the peak power amount of the whole equipment by providing each electrical device with a peak power reduction function such as that described in Patent Document 3. However, it is difficult to set a certain threshold value for the upper limit of the peak power amount such that the peak power amount of the whole equipment may not exceed the upper threshold value through the method of autonomously controlling each electrical device. Therefore, it is necessary to set up a mechanism for managing the power amount of the whole equipment as seen in Patent Document 1 or Patent Document 2.
Nevertheless, it is indispensable to provide the power receiving system described in Patent Document 1 with a large-scale device such as the AC power storage unit. On the other hand, although the power management system described in Patent Document 2 does not need a large-scale device of this kind, electrical devices of high priority and low priority included in the equipment are treated indiscriminately as the peak power reduction objects. In general, reducing the peak power of electrical devices will cause the electrical devices to lower their performances. Therefore, when reducing the peak power amount of the whole equipment in the power management system described in Patent Document 2, the performance of the electrical devices of high priority is lowered in the same manner as that of the electrical devices of low priority.